Generally, steering systems comprise at least a pair of linkages connected to the wheels of the vehicle on which the steering system itself is mounted, a linear actuator, for example electric, provided with a shaft whose ends are associated with said linkages, and a drive mechanism adapted to govern the actuator.
By acting on the drive mechanism it is possible to move the shaft of the actuator toward one or the other wheel by tilting the wheels with respect to the forward direction, in order to steer the vehicle.
A known solution provides that the traversing actuation of the shaft is performed by means of a recirculating ball bearing screw system.
In particular, an outer thread (or more generally an external helical groove) formed on the shaft shell is coupled, through the interposition of balls to a nut screw (understood as a body provided with an internal thread).
The actuation of the shaft is carried out by rotating the nut screw by means of an electric motor: the shaft, not being able to rotate on itself because its ends are hinged to linkages, moves along the axis of rotation of the nut screw.
This type of actuators for steering systems require that the portion of shaft protruding externally from the casing is not equipped with the external thread, otherwise it would not be possible to prevent the ingress of dirt and foreign bodies inside the casing.
For this reason, the shaft portion provided with an external thread has an axial extension limited with respect to the total length of the shaft and must be coupled to a nut screw having an axial extension greater than the axial length of the shaft.
The production of nut screws for steering systems takes place by means of chip removal from an axially hollow cylindrical body which has previously undergone a process of internal adjustment.
In the case in which the cylinder is particularly long, for example because the required length toward the shaft is very high, it is particularly difficult and expensive, if not impossible, to carry out the aforesaid internal adjustment with tolerances reduced adequately.
One purpose of this invention is to solve this drawback of the prior art, in the context of a simple, rational and low-cost solution.
This purpose is achieved by the features of the invention set forth in the independent claim.
The dependent claims outline preferred and/or particularly advantageous aspects of the invention.